Introduce documentation for WSO2 API Management Official Docker images

[chirangaalwis]

Description:
It is required to introduce documentation for WSO2 API Management Official Docker images as per [1].

[1]: Official Docker image review guidelines

[chirangaalwis]

Documentation for for WSO2 API Management Official Docker images have been implemented.

We will update this issue with the relevant PR once it has been opened at docker-library/docs. Hence, closing this issue.

[chirangaalwis]

Please find the relevant PR at docker-library/docs#1496.